1. Field of the Invention
This invention relates to a vulcanizable acrylic elastomer composition, and more particularly to a vulcanizable epoxy group-containing acrylic elastomer composition.
2. Description of the Prior Art
Vulcanizable systems of acrylic elastomers having epoxy groups as cross-linking sites generally contain polyamines, polyamine salts, dithiocarbamates, organic carboxylic acid ammonium salts, imidazoles, etc. as cross-linking agents. However, these vulcanizable systems require a prolonged secondary vulcanization time, because of lower vulcanization rates, as compared with vulcanizable systems of acrylic elastomers containing halogens or active halogens as cross-linking sites, for example, vulcanizable systems containing sulfur or sulfur donor compound-alkali metal salt of fatty acid, trithiocyanuric acid-alkali metal salt of fatty acid, dithiocarbamates, etc. as cross-linking agents, and furthermore they have such disadvantages that the secondary vulcanization products have poor compression set and heat resistance.
However, the acrylic elastomers having epoxy groups as cross-linking sites have such an advantage as a lower metallic corrosion and thus improvements of the vulcanization rate and the compression set have been investigated for the effective utilization of acrylic elastomers having epoxy groups as cross-linking sites.
That is, the following cross-linking agents have been proposed for the vulcanizable system:
Japanese Patent Application Kokai (Laid-open) No. 61-26620 proposes compounds containing at least two carboxyl groups in the molecule-quaternary ammonium salt or phosphonium salt;
Japanese Patent Application Kokai (Laid-open) No. 61-235424 proposes polycarboxylic acid anhydrides-quaternary ammonium salt or phosphonium salt;
Japanese Patent Application Kokai (Laid-open) No. 62-236849 proposes polycarboxylic acids (anhydrides)-quaternary ammonium salt or phosphonium salt-urea;
Japanese Patent Applications Kokai (Laid-open) Nos. 63-57628 and 63-57629 propose organic compounds having at least two --CXNHCY-- bonds (wherein X and Y: O or S) in the molecule-quaternary ammonium salt or phosphonium salt (-compound having a urea bond or thiourea bond); and
Japanese Patent Application No. 63-218752 proposes organic compounds having at least two --CXNHCY-- bonds (wherein X and Y: O or S) in the molecule-guanidine-based compounds.
As to acrylic elastomers having epoxy groups as the cross-linking sites in combination with other cross-linking sites or their vulcanizable systems, the following acrylic elastomers have been proposed:
Japanese Patent Application Kokai (Laid-open) No. 61-26621 proposes acrylic elastomers having epoxy groups and carboxyl groups in combination with the vulcanizable system based on quaternary ammonium salt or phosphonium salt-urea or amide; and
Japanese Patent Application Kokai (Laid-open) No. 61-73708 proposes acrylic elastomers comprising copolymers of acrylic acid ester-dienic monomer-epoxy group-containing vinyl monomer (-monovinylic or monovinylidenic monomer).
However, these acrylic elastomers or their vulcanizable systems also require a secondary vulcanization in order to obtain vulcanization products having a high compression set. Furthermore, changes in the physical properties in the normal state before and after the secondary vulcanization are large and no higher heat resistance is obtained.